<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div id="app">
        <component-a><div slot="header">header</div>
            <div>21321312321</div>
            <div slot="footer"></div></component-a>

    </div>
</body>
<script src="https://cdn.jsdelivr.net/npm/vue@2.6.14/dist/vue.min.js"></script>
<script>
    Vue.component('component-a',{
        render(h){
            console.log(this.$slots.header[0])
            return h('div',{
                class: 'a'
            },this.$slots.header)
        }
    })
    new Vue({
        el: '#app',
components:{

}
    })
</script>

</html>